Anodizing has been used to improve the surface properties of a number of metals, especially aluminum. The anodizing process comprises forming a substantially uniform cohesive oxide layer on the surface of the metal, and in particular aluminum. The objective of the process is to provide a uniform layer of oxide rather than a somewhat non-uniform oxide layer which naturally forms on unprotected aluminum. The anodizing process is relatively straight forward comprising the use of an electrolytic bath and placing the part to be anodized in the bath as an anode. The resulting cohesive oxide layer is substantially harder that the metal itself and can be used to protect and preserve whatever finish has been imparted to the metal, ranging from highly polished to matte. The degree of uniformity of the anodize layer is controlled by its rate of growth and the temperature of the anodize bath. The anodize surface, while reasonably uniform, is known to contain numerous pores which are typically filled in a process known as sealing. Typical sealing processes include the exposure of the oxide surface to hot water or steam to form a aluminum monohydroxide (Boehmite) or exposure to a nickel acetate solution, forming nickel hydroxide, as a sealing agent.
It is often desirable to colour the aluminum oxide layer by using a dye such as any of the commercially available “anodizing dyes” or mineral pigments prior to sealing the surface. By exposing the unsealed anodize layer to these dyes, a migration of the dye species into the oxide pores results. In some cases the dye may be introduced into the electrolytic solution used in the anodize process to dye and anodize concurrently. The subsequent sealing process locks the colour into the pores. Coloured aluminum anodizing has been used in the construction industry for many years. Coloured anodizing also has been used in the manufacture of many finished parts. For example, black anodizing in the automotive industry has been used to prevent reflection from parts used in the military such as binoculars and weapons.
It is also generally well known that the inclusion of infrared or heat absorbing dyes, such as a black dye, into the pores of the oxide layer results in a relative improvement of the heat transmission through the aluminum compared to the heat transmission through an un-dyed anodized surface or an un-anodized surface. This improvement results solely from the absorption of the dye species into the pores of the oxide layer formed by anodizing.
Present method(s) of improving the heat transmission properties of the oxide surface do not consider the effect of the abrupt surface interface created by a highly polished anodized aluminum surface. Further, present processes do not control the degree of gradient of the interfacial region, that is, the region of the interface extending from the outer most anodize-formed oxide surface to the innermost pure aluminum surface, to account for the heat energy to be reflected rather than transmitted. Finally, current processes do account for the properties of the dye used with respect to heat transmission, especially when measured against other desired properties of the dyed surface such as food toxicity, cosmetics, and environmental degradation.
Accordingly, it is an object of the present invention to provide a method for dying the anodized layer to improve the migration of heat absorption species into the pores of the oxide surface produced by anodizing and sealing that dye within the pores. It is a further object of the invention to provide a method for improving the heat transmission properties of an oxide surface of an aluminum plate while at the same time providing on its opposite side of the same plate to create an effective heat reflecting surface or mirror. It is yet another object of the invention to provide novel products using the methods of the present invention to significantly enhance transmission of thermal energy. It is another object of the invention to provide products having superior heat transmission qualities that can be used in contact with eatable products such as prepared foods and drinks.